14 Inspecting the quality of the reception: PX sensors
The TV80 offers a spectrum analyser that shows the signals from each hydrophone. The TV80 allows you to inspect the quality of the received signals from the relevant receiver units. The graph in the Spectrum dialog box provides you with information about the background noise and the signal strength in the selected frequency band.
Context
The quality of the acoustic communication link between the sensors and the receiver can be challenged by noise. When noise appears in the same frequency range as the sensors are using for their communication, the resulting information may be unstable or unreadable. The graph in the Spectrum dialog box provides you with information about the background noise and the signal strength in the selected frequency band. With this information you can identify noise and find the "cleanest" frequencies. On the top and bottom parts of the graph, the channel identifiers correspond to the relevant receiver channel. With the channel identifiers you can easily see in which channels you have signals and noise.
Image
•  The upper scale (PI) identifies the channels for the PI Family receivers.
•  The bottom scale (SR) identifies the channels for the SR Family receivers.
The graph plots data using a 16 colour palette. Red colour corresponds to the maximum value defined, while blue is the minimum.
Note
The Spectrum dialog box can only be used with SR type receiver units:
•  Simrad SR15
•  Simrad SR70
Procedure
1 Verify that one or several hydrophones are connected to the receiver.
2 Open the Setup menu.
3 On the Setup menu, select Spectrum to open the dialog box.
Image
4 Select the hydrophone you want to inspect from the list provided.
5 Set Max Value (the maximum starting value) to 160 dB.
6 Observe the graph in the Spectrum dialog box.
7 Lower the gear monitoring sensor into the water.
Place the sensor on the same depth as the hydrophone, and make sure that the sensor is pointed towards the hydrophone.
8 Verify that the graph in the Spectrum dialog box reflects this.
9 Increase the value of Max Value to reduce the sensitivity and increase the attenuation.
This removes the strong acoustic noise from the presentation.
10 If applicable, repeat the test for each input on the Receiver Unit
11 If applicable, repeat the test for each Receiver Unit